Maven初识

一、概述

Maven 的主要目的是为开发者提供
● 一个可复用、可维护、更易理解的工程综合模型
● 与这个模型交互的插件或者工具

Maven 能够帮助开发者完成以下工作：
● 构建
● 文档生成
● 报告
● 依赖
● SCMs
● 发布
● 分发
● 邮件列表

Maven 工程结构和内容被定义在一个 xml 文件中 － pom.xml，是 Project Object Model (POM) 的简称，此文件是整个 Maven 系统的基础组件

二、安装

http://wiki.jikexueyuan.com/project/maven/environment-setup.html

三、POM

POM 代表工程对象模型。它是使用 Maven 工作时的基本组建，是一个 xml 文件。它被放在工程根目录下，文件命名为 pom.xml。POM 包含了关于工程和各种配置细节的信息，Maven 使用这些信息构建工程。

在创建 POM 之前，我们首先确定工程组（groupId），及其名称（artifactId）和版本，在仓库中这些属性是工程的唯一标识。这些可以在仓库repository中查看到相关信息

下面以java EE的常见 pom.xml为例：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">    <modelVersion>4.0.0</modelVersion>    <groupId>crazyfzw</groupId>    <artifactId>springmvc-demo</artifactId>    <version>1.0-SNAPSHOT</version>    <packaging>war</packaging>    <name>springmvc-demo</name>    <description>springmvc-demo</description>    <!-- 集中定义依赖版本号 -->    <properties>        <junit.version>4.10</junit.version>        <spring.version>4.3.5.RELEASE</spring.version>        <slf4j.version>1.6.4</slf4j.version>        <log4j.version>1.2.17</log4j.version>        <jackson.version>2.8.5</jackson.version>        <mapper.version>2.3.4</mapper.version>        <commons-lang3.version>3.3.2</commons-lang3.version>        <commons-io.version>1.3.2</commons-io.version>        <redis.version>2.9.0</redis.version>        <spring-data-redis.version>1.7.5.RELEASE</spring-data-redis.version>        <jxls-core.version>1.0.6</jxls-core.version>        <poi.version>3.15</poi.version>        <mchange-commons-java.version>0.2.12</mchange-commons-java.version>        <hibernate.version>4.3.9.Final</hibernate.version>        <quartz.version>2.2.3</quartz.version>        <fastjson.version>1.2.22</fastjson.version>        <jstl.version>1.2</jstl.version>        <servlet-api.version>2.5</servlet-api.version>        <jsp-api.version>2.0</jsp-api.version>        <p6spy.version>2.1.4</p6spy.version>    </properties>    <dependencies>        <!-- api -->        <dependency>            <groupId>com.alibaba</groupId>            <artifactId>fastjson</artifactId>            <version>${fastjson.version}</version>        </dependency>        <!-- 单元测试 -->        <dependency>            <groupId>junit</groupId>            <artifactId>junit</artifactId>            <version>${junit.version}</version>            <scope>test</scope>        </dependency>        <!-- Spring -->        <dependency>            <groupId>org.springframework</groupId>            <artifactId>spring-context</artifactId>            <version>${spring.version}</version>        </dependency>        <dependency>            <groupId>org.springframework</groupId>            <artifactId>spring-context-support</artifactId>            <version>${spring.version}</version>        </dependency>        <dependency>            <groupId>org.springframework</groupId>            <artifactId>spring-beans</artifactId>            <version>${spring.version}</version>        </dependency>        <dependency>            <groupId>org.springframework</groupId>            <artifactId>spring-webmvc</artifactId>            <version>${spring.version}</version>        </dependency>        <dependency>            <groupId>org.springframework</groupId>            <artifactId>spring-jdbc</artifactId>            <version>${spring.version}</version>        </dependency>        <dependency>            <groupId>org.springframework</groupId>            <artifactId>spring-aspects</artifactId>            <version>${spring.version}</version>        </dependency>        <dependency>            <groupId>org.springframework</groupId>            <artifactId>spring-orm</artifactId>            <version>${spring.version}</version>        </dependency>        <!-- 日志 -->        <dependency>            <groupId>org.slf4j</groupId>            <artifactId>slf4j-log4j12</artifactId>            <version>${slf4j.version}</version>        </dependency>        <dependency>          <groupId>log4j</groupId>          <artifactId>log4j</artifactId>          <version>${log4j.version}</version>        </dependency>        <!-- Jackson Json处理工具包 -->        <dependency>            <groupId>com.fasterxml.jackson.core</groupId>            <artifactId>jackson-databind</artifactId>            <version>${jackson.version}</version>        </dependency>        <dependency>            <groupId>com.fasterxml.jackson.core</groupId>            <artifactId>jackson-core</artifactId>            <version>${jackson.version}</version>        </dependency>        <dependency>            <groupId>net.sf.json-lib</groupId>            <artifactId>json-lib</artifactId>            <version>2.4</version>            <classifier>jdk15</classifier>        </dependency>        <!-- 通用Mapper -->        <dependency>            <groupId>com.github.abel533</groupId>            <artifactId>mapper</artifactId>            <version>${mapper.version}</version>        </dependency>        <!-- apache-velocity -->        <dependency>            <groupId>org.apache.velocity</groupId>            <artifactId>velocity</artifactId>            <version>1.7</version>        </dependency>        <!--c3p0工具包 -->        <dependency>            <groupId>com.mchange</groupId>            <artifactId>mchange-commons-java</artifactId>            <version>${mchange-commons-java.version}</version>        </dependency>        <!-- Apache工具组件 -->        <dependency>            <groupId>org.apache.commons</groupId>            <artifactId>commons-lang3</artifactId>            <version>${commons-lang3.version}</version>        </dependency>        <dependency>            <groupId>org.apache.commons</groupId>            <artifactId>commons-io</artifactId>            <version>${commons-io.version}</version>        </dependency>        <dependency>            <groupId>commons-fileupload</groupId>            <artifactId>commons-fileupload</artifactId>            <version>1.3.1</version>        </dependency>        <dependency>            <groupId>commons-dbcp</groupId>            <artifactId>commons-dbcp</artifactId>            <version>1.4</version>        </dependency>        <dependency>            <groupId>commons-logging</groupId>            <artifactId>commons-logging</artifactId>            <version>1.1.1</version>        </dependency>        <dependency>            <groupId>commons-beanutils</groupId>            <artifactId>commons-beanutils</artifactId>            <version>1.8.3</version>        </dependency>        <dependency>            <groupId>commons-collections</groupId>            <artifactId>commons-collections</artifactId>            <version>3.2.1</version>        </dependency>        <!-- POI -->        <dependency>            <groupId>org.apache.poi</groupId>            <artifactId>poi</artifactId>            <version>${poi.version}</version>        </dependency>        <dependency>            <groupId>org.apache.poi</groupId>            <artifactId>poi-ooxml</artifactId>            <version>${poi.version}</version>        </dependency>        <dependency>            <groupId>org.apache.poi</groupId>            <artifactId>poi-scratchpad</artifactId>            <version>${poi.version}</version>        </dependency>        <!-- jslx -->        <dependency>            <groupId>net.sf.jxls</groupId>            <artifactId>jxls-core</artifactId>            <version>${jxls-core.version}</version>        </dependency>        <!-- jxl -->        <dependency>            <groupId>net.sourceforge.jexcelapi</groupId>            <artifactId>jxl</artifactId>            <version>2.6.12</version>        </dependency>        <!-- quartz -->        <dependency>            <groupId>org.quartz-scheduler</groupId>            <artifactId>quartz</artifactId>            <version>${quartz.version}</version>        </dependency>        <dependency>            <groupId>opensymphony</groupId>            <artifactId>quartz-all</artifactId>            <version>1.6.1</version>        </dependency>        <!-- hibernate -->        <dependency>            <groupId>org.hibernate</groupId>            <artifactId>hibernate-core</artifactId>            <version>${hibernate.version}</version>        </dependency>        <!-- 连接池 -->        <dependency>            <groupId>p6spy</groupId>            <artifactId>p6spy</artifactId>            <version>${p6spy.version}</version>        </dependency>        <!-- ehcache -->        <dependency>            <groupId>net.sf.ehcache</groupId>            <artifactId>ehcache-core</artifactId>            <version>2.5.1</version>        </dependency>        <dependency>            <groupId>com.oracle</groupId>            <artifactId>ojdbc14</artifactId>            <version>14.0.2.0.4.0</version>        </dependency>        <!-- redis -->        <dependency>            <groupId>redis.clients</groupId>            <artifactId>jedis</artifactId>            <version>${redis.version}</version>        </dependency>        <dependency>            <groupId>org.springframework.data</groupId>            <artifactId>spring-data-redis</artifactId>            <version>${spring-data-redis.version}</version>        </dependency>        <!-- dubbox使用jar -->        <dependency>            <groupId>org.apache.zookeeper</groupId>            <artifactId>zookeeper</artifactId>            <version>3.4.6</version>        </dependency>        <dependency>            <groupId>io.netty</groupId>            <artifactId>netty</artifactId>            <version>3.7.0.Final</version>        </dependency>        <dependency>            <groupId>org.javassist</groupId>            <artifactId>javassist</artifactId>            <version>3.18.2-GA</version>        </dependency>        <dependency>            <groupId>jline</groupId>            <artifactId>jline</artifactId>            <version>0.9.94</version>        </dependency>        <dependency>            <groupId>com.101tec</groupId>            <artifactId>zkclient</artifactId>            <version>0.4</version>        </dependency>        <dependency>            <groupId>com.alibaba</groupId>            <artifactId>dubbo</artifactId>            <version>2.8.4</version>        </dependency>        <!-- https://mvnrepository.com/artifact/joda-time/joda-time -->        <dependency>            <groupId>joda-time</groupId>            <artifactId>joda-time</artifactId>            <version>2.3</version>        </dependency>        <dependency>            <groupId>jstl</groupId>            <artifactId>jstl</artifactId>            <version>${jstl.version}</version>        </dependency>        <dependency>            <groupId>javax.servlet</groupId>            <artifactId>servlet-api</artifactId>            <version>${servlet-api.version}</version>            <scope>provided</scope>        </dependency>        <dependency>            <groupId>javax.servlet</groupId>            <artifactId>jsp-api</artifactId>            <version>${jsp-api.version}</version>            <scope>provided</scope>        </dependency>    </dependencies>    <build>        <sourceDirectory>src</sourceDirectory>        <resources>            <resource>                <directory>src</directory>                <excludes>                    <exclude>**/*.java</exclude>                </excludes>            </resource>            <resource>                <directory>resource</directory>                <excludes>                    <exclude>**/*.java</exclude>                </excludes>            </resource>        </resources>        <plugins>            <plugin>                <artifactId>maven-compiler-plugin</artifactId>                <version>3.1</version>                <configuration>                    <source>1.7</source>                    <target>1.7</target>                </configuration>            </plugin>            <plugin>                <artifactId>maven-war-plugin</artifactId>                <version>2.4</version>                <configuration>                    <warSourceDirectory>WebRoot</warSourceDirectory>                    <failOnMissingWebXml>false</failOnMissingWebXml>                </configuration>            </plugin>        </plugins>    </build></project>

三、仓库：

1) 本地仓库
Maven 本地仓库是机器上的一个文件夹。它在你第一次运行任何 maven 命令的时候创建。
Maven 本地仓库保存你的工程的所有依赖（library jar、plugin jar 等）。当你运行一次 Maven 构建，Maven 会自动下载所有依赖的 jar 文件到本地仓库中。它避免了每次构建时都引用存放在远程机器上的依赖文件。

可以在maven安装地址的conf/settings.xml 指定本地仓库的路径

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0    http://maven.apache.org/xsd/settings-1.0.0.xsd">      <localRepository>E:/myLocalRepository</localRepository></settings>

2）中央仓库
http://mvnrepository.com/
https://search.maven.org/

3)远程仓库
可以在私有服务器上搭建自己的maven仓库，外网的内网的都可以。eg:

  <repositories>      <repository>         <id>companyname.lib1</id>         <url>http://download.companyname.org/maven2/lib1</url>      </repository>      <repository>         <id>companyname.lib2</id>         <url>http://172.16.176.234/maven2/lib2</url>      </repository>   </repositories>

Maven 依赖搜索顺序
步骤1：在本地仓库找
步骤2：若本地仓库没找到则去中央仓库找，找到则下载到本地仓库，留着日后备用
步骤3：若中央仓库没找到，则会检查时候有设置远程仓库，若有，则会在远程仓库中查找并下载到本地仓库备用。若没设置远程仓库或者在远程仓库中也无法找到，则会抛出错误(无法找到依赖的文件)

针对这种情况，可以通过构建外部依赖的方法解决。

四、构建外部依赖

把jar包文件并放到工程lib下，然后在pom.xml中添加依赖，eg:

<project xmlns="http://maven.apache.org/POM/4.0.0"        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"       xsi:schemaLocation="http://maven.apache.org/POM/4.0.0        http://maven.apache.org/maven-v4_0_0.xsd">       <modelVersion>4.0.0</modelVersion>       <groupId>com.companyname.bank</groupId>       <artifactId>consumerBanking</artifactId>       <packaging>jar</packaging>       <version>1.0-SNAPSHOT</version>       <name>consumerBanking</name>       <url>http://maven.apache.org</url>      <dependencies>          <dependency>             <groupId>ldapjdk</groupId>             <artifactId>ldapjdk</artifactId>             <scope>system</scope>             <version>1.0</version>             <systemPath>${basedir}\src\lib\ldapjdk.jar</systemPath>          </dependency>       </dependencies>    </project>

五、依赖管理(Maven的核心特点之一)

当一个库 A 依赖于其他库 B. 另一工程 C 想要使用库 A, 那么该工程同样也需要使用到库 B。

使用maven，我们只需要在每个工程的 pom 文件里去定义直接的依赖关系。Maven 则会自动的来接管后续的工作。比如我们在pom.xml中定义了依赖jar包A，那么A所依赖的其他jar包，会被自动下载，不需要我们去定义。是不是很省事？

本文只是初步介绍了下maven 的使用，主要是在maven管理jar包，pom.xml文件的配置方面。还没涉及到maven在项目管理以及自动化构建方面。可参考下面链接拓展学习。

Apache Maven 入门篇

Maven - 构建自动化

转载请注明出处: http://blog.csdn.net/FZW_Faith/article/details/54728943